Chimney 101: Diagrams and Glossary of Terms

ANATOMY
OF A MASONRY CHIMNEY

Chimney Cap (not shown on this illustration): Chimney caps cover the top opening of the flue for the purpose of keeping out rain and snow. Moisture is the number one cause of chimney and fireplace deterioration. The chimney cap is also a spark arrestor which keeps sparks and cinders from landing on the roof. Chimney caps also keep out animals, leaves and other debris.

Chimney Crown (wash or splay): The chimney crown is the cast concrete or mortar at the top of the

chimney that seals off the air space between the outer walls of the masonry chimney and the flue liner and prevents water entry into the stack. The cement crown slopes away from the flue to wash the water away.

Flue: A safe pathway for heat and combustion by-products through the construction of the home; otherwise known as the interior of the chimney.

Chimney Liner: The safe, approved material that lines the flue's interior. This material should be 5/8" or thicker terracotta tiles or a UL listed liner made of stainless steel or other approved materials.

Chimney:The structure that passes through the construction of the home and encloses the flue (or flues).

Smoke Chamber:The dome area of brick corbels that supports the flue tiles and directs flue gases safely to the flue. This area should be parge coated with super cement to provide a smooth transition to the flue (draft performance), protect the masonry and prevent cinders, heat/fire and carbon monoxide from entering the home through voids in otherwise exposed brick and mortar.

Smoke Shelf:The area located behind the damper that prevents down drafts from coming into the firebox area and home. This throat design also increases the velocity of the flue gasses which helps draft performance.

Damper: The damper closes off the fireplace from the outside of the house. This is what prevents air loss from your home when the fireplace is not in use. In some cases the damper can be used to regulate the chimney's draft.

Mantel:Typically a decorative shelf above a fireplace. May also be a beam, stone or arch that serves to support the masonry above the fireplace.

Lintel:The horizontal architectural member or header above the fireplace opening that provides the support for the brickwork above the fireplace opening.

Fire Brick:Heat resistant brick that lines the firebox or combustion area of a fireplace, stove, boiler or furnace.

Ash Dump:An opening located in the inner-hearth of some fireplaces, which leads to an ash pit for convenient ash removal and fireplace cleaning.

Ash Pit: A cavity underneath a fireplace firebox used as a receptacle for ashes, and is accessible for clean-out by way of a clean-out door located outside the home or, in some cases, in a basement.

Firebox : This is where you build the fire; also known as the interior of the fireplace.

Inner Hearth: The floor of the fireplace, inside the opening.

Outer Hearth or Hearth Extension: This is the technical term for what is usually referred to as the hearth. It is the non-combustible floor area in front of the fireplace that is required for safety. NFPA code requires the outer hearth to extend 18" from the fireplace opening.

Top-sealing Damper: Also known as a chimney top damper. Damper mounted at top of flue used as an alternative to a throat damper and is also an energy-saving device.

TYPICAL FACTORY BUILT "ZERO CLEARANCE CHIMNEY AND FIREPLACE

Termination Cap or Chimney Cap:The last piece of the top most part of a factory-built chimney pipe system, which serves the purpose of arresting sparks, keeping water out of the flue, and providing an outlet for cooling air on air-cooled chimney system.

Chase Cover (bottom pan):A custom-made flashing that keeps water out of the chimney chase and home while providing an opening for the pipe termination.

Chase:A pathway for a manufactured chimney pipe to pass through. Chases are commonly built on the home to resemble a traditional chimney, to provide lateral support for the chimney pipe, and keep the cold weather from cooling the flue.

Firestop / Firestop Spacer:A manufactured component of a factory-built chimney that separates the fireplace enclosure from the attic areas and still allows proper heat clearances to adjacent combustibles. This slows the spread of fire through a home in the instance of a house fire and is required by building code.

Chimney:The structure that passes through the construction of the home and encloses the flue (or flues).

Fireplace:This is the firebox or place where you build the fire or place the gas logs.

Hearth:The non-combustible floor area in front of the fireplace that is required for safety. NFPA code requires the outer hearth to extend 18" from the fireplace opening.

Ceiling Support / Chimney Support:Generally the first piece of chimney that is fastened to the framing of the house and supports the entire weight of the chimney system. The bottom side often has a decorative collar and is exposed in the home's interior.